This study proposes to examine the role of fresh syngeneic bone marrow in the incorporation of frozen orthotopic bone allografts. A diaphyseal cortical femoral graft model in inbred rats will be studied. The immune response to frozen bone exchanged across weak and strong transplantation barriers with emphasis on the possible suppressors of the response will be determined. Parameters of quantitative morphology, isotopic kinetics and mechanical characteristics will be investigated. Quantitative histologic techniques will use in vivo fluorescent labelling and image analyses. The isotopic kinetics of bone formation and resorption of the allograft will be analyzed by using 45 calcium, 3H-tetracycline and 3H-proline. The material and geometric properties of bone obtained by torsional testing and histomorphometry will be correlated with the other parameters. The presence of cell-mediated and humoral cytotoxicity after bone allografting will be evaluated. Hypo- and hyper-responsiveness to bone allografts will be investigated in vivo by an ovarian graft assay and in vitro by mixed lymphocyte and cell-mediated cytotoxicity reactions. The correlation of the mechanical, morphologic and metabolic parameters with the immune responses will quantify both bone repair and the immune effect of bone marrow containing bone allografts so that the best possible circumstances for a successful bone graft may be defined.